Seal for hydropneumatic pressure intensifier

ABSTRACT

The invention relates to a hydropneumatic pressure intensifier comprising a radial seal ( 24, 27 ). Said seal is arranged between working pistons ( 2 ) and the cylinder bore which accommodates said pressure intensifier or in a bore hole ( 15 ) between the working chamber ( 3 ) and a storage area ( 14 ), whereby the radial seals consist of viscoplastic and flexible synthetic material.

BACKGROUND OF THE INVENTION

The invention concerns a hydropneumatic pressure intensifier of the typecategorizing the main claim. Hydropneumatic pressure intensifiers ofthis type are used mainly for machine tools and function withalternating pressures, i.e. high pressure and low pressure in theworking chamber, and having pneumatic and hydraulic working meansexhibiting alternating rapid pressure increases and changes betweenoverpressure and underpressure. This affects in particular the sealingrings of the seals between the working piston and the cylindrical wallof the working chamber and/or the sealing ring in the connecting borebetween the working chamber and the storage chamber, wherein, at lowpressure, the plunger piston is repeatedly introduced into and removedout of the sealing ring. This plunging process requires appropriatedesign of the sealing ring to ensure that when the plunger piston isimmersed, the end face of the plunger piston does not clamp on thesealing ring side facing same, wherein the radial forces produced by therubber-elastic tensioning ring, which have a corresponding effect on theclearance of the sealing ring, have to be taken into consideration. Thesealing ring must have an appropriately large radial stiffness andguarantee static and dynamic sealing. The sealing ring must, of course,have high wear resistance and extrusion resistance with long servicelife and should facilitate assembly without deformation of the sealingedges. The sealing ring must, in particular, resist extremely highloads, i.e. high pressures and pressure shocks.

A known hydropneumatic pressure intensifier of the type categorizing theinvention (EP 0 579 073 B1 and DE-PS 32 25 906 C2) provides the optimumpreconditions for the expert, in particular for the producer of thepatented sealing ring. It is thereby assumed that the high pressure candirectly act on the sealing ring from one side. Due to the step providedin the direction of the working chamber on the circumferential surfaceof the sealing ring facing the piston, this sealing ring is axiallyloaded and pressed against the end wall, facing away from the workingchamber, of the annular groove receiving the sealing ring withoutproducing actual deformation of the sealing ring to thereby provide theintended sealing support of the sealing surface on the piston surface.Other sealing rings produced by this sealing ring manufacturer which aremade from softer distortable material would not be used by one ofaverage skill in the art, since their radial stiffness is either too lowfor immersion or they cannot withstand the high pressures and dynamicwear.

Practice has moreover shown that the above-mentioned sealing ring usedfor hydropneumatic pressure intensifiers consists of a material which isdistributed under the trademark Turcon T46 which has metallic inclusionsproducing increased friction between the sealing ring and piston whichact like sanding dust at this location. These metallic inclusions mayalso be caused by friction on the piston due to the hardness of thesealing material. This has, in end effect, the same result as sandingdust and guarantees good sealing and durability or service life due tothe structure of the sealing ring while reducing wear on the piston inthe sealing area.

SUMMARY OF THE INVENTION

In contrast thereto, the inventive hydropneumatic pressure intensifierhaving the characterizing features of the main claim (in contrast to theexpectations of one of average skill in the art and despite the expectedrelatively easy incorporation of the sealing ring due to the associatedpressure and friction acting on the piston) not only advantageouslyprovides good sealing and durability, i.e. service life, but alsoprevents wear in the frictional area between the sealing ring and pistonsurface. Moreover, in contrast to the expectations of one of averageskill in the art, immersion of the plunger piston into the sealing ringis very easy although, due to the increased softness, the sealing ringcan be deformed by the tensioning ring in the direction of the sealingsurface. Such a relatively soft sealing ring with correspondingcross-sectional design is known per se (EP 0 670 444) as is the typicaldeformation of this sealing ring (EP 0 582 593). The material used isdistributed by the producer under the trademark Zurcon: the sealing ringitself under the trademark Rimseal. The producer recommends use of thisseal only as a secondary seal especially for relatively high pressures.It was developed explicitly as such and only in this way can safesealing of thin oil films be guaranteed, in particular, with lowsecondary pressures. The material is polyurethane with Shore D 58. Oneof average skill in the art uses such a sealing ring in particular ifthe piston exhibits a slight tilting movement with respect to itscylinder. Immersion of a plunger piston into such a soft material is notconsidered to be acceptable by one of average skill in the art. Theabove-mentioned relatively hard sealing ring is recommended for theprimary seal and is used in conventional hydropneumatic intensifiers.Due to the relatively soft material, which is also absolutely free frommetallic inclusions, the piston surface is not subjected to frictionalwear which could lead to the above-mentioned sanding dust effect.

In accordance with an advantageous embodiment of the invention, theopposite walls of the annular groove or the like extend essentiallyparallel to one another. As a result thereof, the sealing ring is loadedwith unilateral forces produced by the conical travel of the end walland acting in the direction of the piston.

In accordance with a further advantageous embodiment of the invention,the plastic material of the sealing ring does not have any metallicinclusions. This has the principal advantage of preventing mechanicalwear of the piston surface.

In accordance with another advantageous embodiment of the invention, thesealing ring consists of a plastic material produced by the companyBusak and Shamban under the name Zurcon with the trademark Rimseal andmade from a special polyurethane 58 Shore B.

In accordance with another advantageous embodiment of the invention, theworking piston comprises a pneumatically loaded collar for its faststroke drive, wherein the rear side of the seal is alternately loadedwith pneumatic working pressure and with the lowermost pressure.

In accordance with another advantageous embodiment of the invention, thesealing ring is directly loaded at the working chamber side with thepressure of the working chamber, without any other intermediate sealingelements.

BRIEF DESCRIPTION OF THE DRAWING

Further advantages and advantageous embodiments of the invention can beextracted from the following description, the drawing and the claims.

One embodiment of the subject matter of the invention is shown in thedrawing and explained in more detail in the following:

FIG. 1 shows a longitudinal section through a hydropneumatic pressureintensifier;

FIG. 2 shows each a section in the area of a radial seal of FIG. 1, inan enlarged scale

FIG. 3 shows a section in the area of a radial seal of FIG. 1, in anenlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the hydropneumatic pressure intensifier shown in FIG. 1, a workingpiston 2 is disposed in a casing 1 in an axially displaceable andradially sealed manner and delimits therewith a working chamber 3 filledwith hydraulic oil. A piston rod 4 is disposed on the working piston 2and projects beyond the casing 1. The working piston 2 further comprisesan auxiliary piston 5 shaped as a collar which is radially sealedtowards the tubular shell 6 and thereby separates two pneumatic chambers7 and 8 which are supplied alternately with air pressure for the faststroke of the working piston 2. As soon as the air pressure in thepneumatic chamber 7 is sufficiently high and the pressure in thepneumatic chamber 8 is sufficiently low, the working piston 2 is pusheddownward. Conversely, with corresponding high pressure in the pneumaticchamber 8 and reduced pressure in the pneumatic chamber 7, the piston 2is displaced again in the initial position shown.

The working chamber 3 is closed on the side facing away from the piston2 by a casing part 9 to which a tubular shell 11 is attached which, inturn, is closed by a casing lid 12. A storage piston 13 is disposed inthe tubular shell in an axially movable fashion and delimits a storagechamber 14 along with the tubular shell 11 and casing part 9. Thisstorage chamber 14 is hydraulically connected to the working chamber 3via a plunger bore 15 disposed in the casing part 9. A drive piston 16is also disposed in the tubular shell 11 in a radially sealed fashionfor actuating a plunger piston 17 and is loaded by a storage spring 18which is supported on the storage piston 13 on the side facing away fromthe drive piston 16 and thus determines the storage pressure present inthe storage chamber 14 and serves as a restoring force for the drivepiston 16. The spring chamber 19 accommodating the spring 18 ispressure-relieved. A driving chamber 21 is disposed on the side of thedrive piston 16 facing away from the spring chamber 19 and can besupplied, via a connection 22, with pressurized air to drive the drivepiston 16.

The plunger piston 17 is axially displaceably guided in a central bore23 of the storage piston 13, wherein a radial seal 24 prevents hydraulicoil from passing from the storage chamber 14 into the spring chamber 19.A radial seal 25 is disposed in an annular groove 26 in the surfaceregion of the plunger piston 13 and seals towards the tubular shell 11to also prevent hydraulic oil from reaching the spring chamber 19.

During its driving motion in the direction of the arrow I, effected bythe pressurized air in the driving chamber 21, the plunger piston 17penetrates the plunger bore 15 thereby separating the storage chamber 14from the working chamber 3. To achieve absolute separation, a radialseal 27 is disposed in the wall of the plunger bore 15. (Shown in FIG. 2in an enlarged scale). As soon as the plunger piston 17 is immersed inthe working chamber 3, the hydraulic fluid therein is displaced, therebyproducing corresponding pressure intensification of the air pressureprevailing in the driving chamber 21 relative to the hydraulic pressureprevailing in the working chamber 3 in accordance with thecross-sectional ratio between the drive piston 16 and plunger piston 17.Due to the relatively large cross-sectional surface of the workingpiston 2, a correspondingly large actuating force for the piston rod 4is produced in accordance with the hydraulic pressure in the workingchamber 3. To be able to maintain the pressure in the working chamber 3,and to prevent hydraulic fluid from passing from the working chamber 3into the pneumatic chamber 7, a radial seal 29 is disposed in an annulargroove 28 in the casing 1. (Shown in FIG. 3 in an enlarged scale). Thecasing 1 further comprises two annular toroidal sealing rings 31 whichseal towards the working piston 2.

As shown in FIG. 2, the plunger bore 15 has a step 32 facing the workingchamber 3 into which a support ring 33 is introduced and axially securedby a retaining ring 34. The radial seal 27 is disposed between thesupport ring 33 and the end wall 35 of the step and consists of asealing ring 36 and a tensioning ring 37 pressing the sealing ring 36against the plunger piston 17. The tensioning ring 37 is an annulartoroidal sealing ring which assumes an oval shape in the installedposition. The sealing ring 36 consists of special, relatively softpolyurethane with 58 Shore D. Viewed in cross-section, the circumference38 extends parallel to the plunger piston 17. The pressing force of thetensioning ring 37 produces a sealing surface 39 towards the surfacearea of the plunger piston 17. A gradation 41 is provided in the sealingring 36 facing the pressure chamber 3, thereby pressing the sealing ring36 against the end wall 35 when the working chamber 3 is at highpressure, wherein the associated element flank 42 abuts against the endwall 35 although it extends, in the pressure-less condition or at lowpressures in the working chamber 3, at an angle with respect to the endwall 35. This deformation at high pressures effects increased pressingin the area of the sealing surface 39. The sealing ring has a conicalsurface 43, having a small wedge angle, between element flank 42 andsealing surface 39 which serves mainly to ensure that, with low storagepressure and largely undeformed sealing ring 36, the plunger piston 17can easily penetrate through the sealing ring 36 when passing throughthe plunger bore 15. When the plunger piston 17 first contacts theconical surface 43, the sealing ring 36 is displaced in the direction ofthe support ring 33 and largely without deformation of the sealing ring36 since, at the beginning of immersion, the hydraulic pressure on bothsides of the sealing ring is approximately equal. Subsequently, thepressure in the working chamber 3 rapidly increases to thereby move thesealing ring 36 into the position shown and then into the deformationposition. During the return stroke of the plunger piston 17, thepressure in the working chamber may be lower than that in the storagechamber 14 such that the sealing ring 36 is displaced into the positionshown due to the frictional engagement between plunger piston 17 andsealing ring 36. Also in this case, no substantial deformation occurs.

The radial seal 29, disposed in the annular groove 28, between workingpiston 2 and casing 1 of FIG. 3 is basically of the same construction. Atensioning ring 44 acts radially on a sealing ring 45. The sealing ring45 has a nearly rhombic cross-section with a gradation 46 facing theworking chamber 3 and is supported, with a sealing surface 47, on thesurface area of the piston 2. As soon as the pressure in the workingchamber 3 is high enough, the element flank 48 of the sealing ring 45 ispressed against the end wall 49 of the annular groove 28 therebyincreasing the pressing force of the sealing surface 47 and enhancingperformance through the frictional engagement between piston 2 andsealing ring 45. The sealing ring 45 is thereby deformed considerablydue to its relatively soft material, wherein, in particular, thecircumferential area 51, parallel to the piston, is also displaced intoa slightly conical disposition. As soon as the working piston 2 startsits return stroke and the pressure in the working chamber 3 is low oreven at underpressure, the sealing ring 45 assumes its previous shapedue to frictional engagement and is displaced in the direction of theworking chamber 3 up to the other end wall of the annular groove 28. Thesealing ring 45 assumes its initial shape and is not deformed again,since the underpressure is too low.

All the features mentioned in the description, the following claims andshown in the drawing may be essential to the invention eitherindividually or in any arbitrary combination.

LIST OF REFERENCE NUMERALS

1 casing

2 working piston

3 working chamber

4 piston rod

5 auxiliary piston

6 tubular shell

7 pneumatic chamber

8 pneumatic chamber

9 casing part

10

11 tubular shell

12 casing lid

13 storage piston

14 storage chamber

15 plunger bore

16 drive piston

17 plunger piston

18 storage spring

19 spring chamber

20

21 driving chamber

22 connection

23 central bore

24 radial seal

25 radial seal

26 annular groove

27 radial seal

28 annular groove

29 radial seal

30

31 annular toroidal sealing ring

32 step

33 support ring

34 retaining ring

35 end wall

36 sealing ring

37 tensioning ring

38 circumferential surface

39 sealing surface

40

41 gradation

42 element flank

43 cone surface

44 tensioning ring

45 sealing ring

46 gradation

47 sealing surface

48 element flank

49 end wall

50

51 circumferential surface

I driving direction

I claim:
 1. A hydropneumatic pressure intensifier comprising: anapparatus casing having a cylindrical working chamber for acceptingvarying pressure, said varying pressure including a low storage pressureand a high working pressure; a working piston delimiting an end face ofsaid working chamber, said working piston actuated by said workingpressure to effect a working stroke, said working piston guided foraxial displacement and radial sealing with respect to a cylindrical wallof said working chamber; a tubular shell having a storage chamber, saidstorage chamber in hydraulic communication with said working chamber,wherein, during a fast working stroke and in response to said storagepressure, hydraulic oil flows from said storage chamber into saidworking chamber and wherein, during a return stroke, hydraulic oil flowsback into said storage chamber; a plunger piston, said plunger pistonactuated as a high pressure generator via at least one of pneumaticmeans and hydraulic means, said plunger piston immersed within saidworking chamber after said fast working stroke of said working piston; aplunger bore disposed between said storage chamber and said workingchamber, said plunger bore aligned with said plunger piston, saidplunger piston moving into and through said plunger bore for introducingsaid working stroke, wherein said plunger piston is guided in a radiallysealed and axially displaceable fashion; and a dynamic radial sealdisposed in an annular groove of said plunger bore proximate saidplunger piston, said radial seal consisting essentially of a stationaryrubber-elastic tensioning ring and an elastic plastic sealing ringdisposed between said tensioning ring and said plunger piston, wherein afirst circumferential surface of said sealing ring facing said workingchamber and said plunger piston has a gradation, a secondcircumferential surface of said sealing ring facing a low pressure sideand said plunger piston has a conical surface which opens at a smallwedge angle, and a third surface of said sealing ring defines achanging, conical separation from a first end wall of said annulargroove facing away from said working chamber, wherein a sealing surfaceof said sealing ring is disposed between said gradation and said conicalsurface, wherein, independent of a relative direction of motion betweensaid plunger bore and said plunger piston, said third surface of saidsealing ring is pressed, during said working stroke, by existing workingpressure, with a reduction in said changing, conical separation towardssaid first end wall, wherein said sealing ring, said tensioning ring,said plunger bore, said annular groove, and said plunger piston aredimensioned and structured such that said sealing surface substantiallydeforms and widens when said plunger piston enters into said plungerbore without substantial deformation of other portions of said sealingring, with said sealing ring subsequently substantially maintaining itsshape while said plunger piston moves within said plunger bore.
 2. Thepressure intensifier of claim 1, wherein said first end wall of saidannular groove is substantially parallel to a second end wall of saidannular groove.
 3. The pressure intensifier of claim 1, wherein saidplastic material of said sealing ring does not have any metallicinclusions.
 4. The pressure intensifier of claim 1, wherein said sealingring consists of plastic material made from polyurethane 58 Shore D. 5.The pressure intensifier of claim 4, wherein said plastic material isZurcon®.
 6. The pressure intensifier of claim 4, wherein said plasticmaterial is Rimseal®.
 7. The pressure intensifier of claim 1, whereinsaid working piston comprises a pneumatically loaded collar for its faststroke drive.
 8. The pressure intensifier of claim 1, wherein saidsealing ring is directly loaded by pressure in said working chamber,without any other intermediate sealing elements.
 9. The pressureintensifier of claim 1, wherein a same sealing ring is disposed in bothsaid plunger bore as well as in said cylindrical wall of said workingchamber facing said working piston.
 10. The pressure intensifier ofclaim 1, further comprising a second dynamic radial seal disposed in asecond annular groove of said cylindrical wall of said working chamberproximate said working piston, said second radial seal consistingessentially of a second stationary rubber-elastic tensioning ring and asecond elastic plastic sealing ring disposed between said secondtensioning ring and said working piston, wherein a first circumferentialsurface of said second sealing ring facing said working chamber and saidworking position has a gradation, a second circumferential surface ofsaid second sealing ring facing a low pressure side and said workingpiston has a conical surface which opens at a small, conical angle, anda third surface of said sealing ring defines a changing separation froma first end wall of said second annular groove facing away from saidworking chamber, wherein a sealing surface of said second sealing ringis disposed between said second ring gradation and said second ringconical surface, wherein, independent of a relative direction of motionbetween said second annular groove and said working piston, said thirdsurface of said second ring is pressed, during said working stroke, byexisting working pressure, and with a reduction in said changing,conical separation towards said first end wall of said second annulargroove.